The present invention is generally directed to detecting faulty nozzles in an ink jet print head. More particularly, the invention is directed to automatically printing and inspecting a test pattern to detect whether any nozzles have malfunctioned.
Ink jet printers form images on paper by ejecting ink droplets from an array of nozzles on a print head. During the operational lifetime of an ink jet print head, the nozzles can become clogged, thus blocking the ejection of ink from the nozzles. Although most current ink jet printers include mechanisms for clearing clogged nozzles, these mechanisms are not always successful, and nozzles remained clogged.
Generally, when printer driver software generates print data to be sent to the print head, the software typically assumes that all of the nozzles of the print head are functioning properly. Thus, the print data may address nozzles that are malfunctioning. If this be the case, pixels that should be printed by the malfunctioning nozzles will remain blank on the paper. The typical result is an unwanted horizontal strip of white space in a printed image. As more and more nozzles malfunction during a print head""s lifetime, this situation becomes more and more noticeable in printed output.
Therefore, a system is needed for identifying malfunctioning ink jet nozzles and providing this information to a printer driver so that the printer driver can compensate for the malfunctioning nozzles when generating print data.
The foregoing and other needs are met by an apparatus for detecting faulty nozzles in an ink jet printer. The apparatus includes processor means for receiving print data and for generating print commands, scan commands, and advance commands based on the print data. The apparatus also includes an ink jet print head having a plurality of ink jet nozzles disposed adjacent a print medium. The print head receives the print commands from the processor means and ejects ink droplets from each of the nozzles separately and sequentially during discrete printing periods in response to the print commands, where only one nozzle prints during a discrete printing period. Thus, the apparatus prints individual test images corresponding to each nozzle. The test images are printed at test image positions which are separated from a reference position by corresponding predetermined reference distances.
The apparatus also includes a print head scan mechanism for receiving the scan commands from the processor means. In response to the scan commands, the print head scan mechanism moves the print head in a first direction relative to the print medium during the discrete printing periods. The apparatus has a print medium advance mechanism for moving the print medium in a second direction during a time interval occurring between the printing of the test images, where the second direction is orthogonal to the first direction. In this manner, the apparatus leaves nonprinted areas on the print medium between the individual test images.
The apparatus has a fixed optical sensor which is positioned adjacent the print medium and which is nonmovable in the first direction relative to the print medium. The optical sensor detects light reflected from the print medium and generates a sensor signal based thereon. The sensor generates the sensor signal indicating a first state when the sensor detects light reflected from one of the test images. The sensor generates the sensor signal indicating a second state when the sensor detects light reflected from one of the nonprinted areas.
After the apparatus prints the test images, the print medium advance mechanism moves the print medium in the second direction relative to the optical sensor, thereby causing the test images on the print medium to move sequentially adjacent the optical sensor in the second direction. As the print medium moves in the second direction relative to the optical sensor, the processor means receives the sensor signal from the sensor. When the optical sensor is adjacent a test image position and the sensor signal does not indicate the first state, the processor generates a fault signal.
Thus, the present invention prints a test image corresponding to each nozzle on the print head, and detects the test images using a fixed optical sensor, such as a typical media sensor. Since each nozzle is supposed to print a test image at a particular location, a missing test image indicates a malfunctioning nozzle. Further, the position of the missing test image relative to the reference position indicates which nozzle has malfunctioned. Since the test pattern is inspected automatically by the optical sensor, a user does not have to visually inspect a printed sample to detect faulty nozzles.
The use of a fixed optical sensor is advantageous since there is no need to place a sensor on a movable carriage. Further, there is no need to provide flexible electrical lines such as would be required to connect a movable sensor to circuits in the printer. Thus, the use of the fixed optical sensor to detect faulty nozzles significantly simplifies the design and reduces the cost of the printer as compared to a system that uses a scanning sensor.